1. Field of the Invention
The present invention relates to a CMP (chemical mechanical polishing) apparatus that polishes wafers in the manufacturing process of semiconductor devices, and a dresser that reconditions a polishing pad provided in a CMP apparatus.
2. Description of the Related Art
The surface of a polishing pad is worn down during wafer polishing in the CMP process and, therefore, it is inevitable to perform reconditioning by the use of a dresser. Under the present circumstances, one dresser is arranged for one polishing pad and reconditioning is performed by causing the polishing pad and the dresser to rotate on their own axes.
FIG. 1 is a sectional view of a CMP apparatus of a related art in which one dresser is arranged, and FIG. 2 is a plan view of FIG. 1. As shown in these figures, the CMP apparatus has polishing head 1 that produces a polishing action by pushing the surface of wafer 2 against polishing pad 5. Polishing head 1 is provided with retainer ring 3 that holds wafer 2 that is being polished and is provided with membrane 4 that applies pressure to a rear surface of wafer 2 that is being polished. In order to ensure that the whole surface of semiconductor wafer 2 is evenly depressed onto the surface of polishing pad 5, polishing head 1 is also provided with periphery pressurizing portion 6 that pressurizes the periphery of wafer 2. During polishing, a rotational motion is given to polishing head 1, and also polishing pad 5 is rotatably driven around a center portion of the polishing pad.
A slurry supply port 7 that supplies slurry (an abrasive) is present on the polishing pad 5 and a dresser 8 that reconditions the polishing pad 5 is also arranged thereon.
To recondition polishing pad 5, this dresser 8 oscillates on polishing pad 5 in the range of the radius of polishing pad 5 while rotating on its own axis as shown in FIG. 2, thereby performing the cutting of polishing pad 5. For this reason, the reconditioning time becomes long in proportion to the size of polishing pad 5 and the dresser life relative to the number of treated wafers decreases.
To extend the life of a polishing pad and stabilize the polishing rate, Japanese laid-open patent publication No. 11-48122 proposes a technique for using two kinds of dressers for one polishing pad as a related art.
However, conventional CMP apparatus have had the following problems.
The dresser reconditions the polishing pad by cutting the polishing pad while oscillating within the radius of the polishing pad in the spare time when the wafer is being conveyed before and after polishing. For this reason, the larger the diameter of the polishing pad, the longer the required reconditioning time will be, and the throughput of the CMP apparatus will decrease by just that much.
Also, when a dresser is used, the edge of diamond abrasive grains fixed to a bottom surface of the dresser becomes dull and the cutting capacity of the polishing pad decreases. When the polishing pad diameter increases, the cutting time becomes long and, therefore, the cumulative number of treated wafers per dresser decreases. Furthermore, it is necessary that dresser replacement be performed in accordance with the procedure of replacement work, simulation polishing and checking the polishing rate/uniformity of polishing/dust/scratches and the like, and the apparatus comes to a stop for about 4 hours once the replacement is made. Therefore, it follows that the apparatus stop time (downtime) also increases with increasing frequency of dresser replacement.